public DiscardInfo isObviousStatically(VarInfo[] vis) {

    VarInfo subvar = var1(vis);
    VarInfo supervar = var2(vis);

    // check for x[i..j] subsequence of x[]
    VarInfo subvar_super = subvar.isDerivedSubSequenceOf();
    if (subvar_super == supervar) {
      debug.fine("  returning true because subvar_super == supervar");
      return new DiscardInfo(this, DiscardCode.obvious, "x[i..j] subsequence of x[] is obvious");
    }

    Object[] obv1 = SubSequence.isObviousSubSequence(subvar, supervar);
    if (obv1[1] != null) {
      return new DiscardInfo(this, (DiscardCode) obv1[0], (String) obv1[1]);
    }

    // JHP: This is not a valid obvious check, since it  doesn't imply that
    // the invariant is true.
    if (!subvar.aux.getFlag(VarInfoAux.HAS_ORDER) || !supervar.aux.getFlag(VarInfoAux.HAS_ORDER)) {
      // Doesn't make sense to consider subsequence if order doens't matter
      return new DiscardInfo(
          this, DiscardCode.obvious, "Order doesn't matter, so subsequence is meaningless");
    }

    return super.isObviousStatically(vis);
  }
  // (Seems overkill to check for other transitive relationships.
  // Eventually that is probably the right thing, however.)
  public DiscardInfo isObviousDynamically(VarInfo[] vis) {

    // System.out.println("checking isObviousImplied for: " + format());
    if (debug.isLoggable(Level.FINE)) {
      debug.fine("isObviousDynamically: checking " + vis[0].name() + " in " + vis[1].name());
    }

    DiscardInfo super_result = super.isObviousDynamically(vis);
    if (super_result != null) {
      return super_result;
    }

    VarInfo subvar = var1(vis);
    VarInfo supervar = var2(vis);

    // JHP: The next check is an un-interesting check, not
    // an obvious check.  We need to figure out how to resolve this.

    // Uninteresting if this is of the form x[0..i] subsequence
    // x[0..j].  Not necessarily obvious.
    VarInfo subvar_super = subvar.isDerivedSubSequenceOf();
    VarInfo supervar_super = supervar.isDerivedSubSequenceOf();
    if (subvar_super != null && subvar_super == supervar_super) {
      debug.fine("  returning true because subvar_super == supervar_super");
      return new DiscardInfo(
          this, DiscardCode.obvious, "x[0..i] subsequence of x[0..j] is uninteresting");
    }

    if (isObviousSubSequenceDynamically(this, subvar, supervar)) {
      return new DiscardInfo(
          this,
          DiscardCode.obvious,
          subvar.name() + " is an obvious subsequence of " + supervar.name());
    }
    return null;
  }
  /**
   * Returns true if the two original variables are related in a way that makes subsequence or
   * subset detection not informative.
   */
  public static boolean isObviousSubSequenceDynamically(
      Invariant inv, VarInfo subvar, VarInfo supervar) {

    VarInfo[] vis = {subvar, supervar};

    ProglangType rep1 = subvar.rep_type;
    ProglangType rep2 = supervar.rep_type;
    if (!(((rep1 == ProglangType.INT_ARRAY) && (rep2 == ProglangType.INT_ARRAY))
        || ((rep1 == ProglangType.DOUBLE_ARRAY) && (rep2 == ProglangType.DOUBLE_ARRAY))
        || ((rep1 == ProglangType.STRING_ARRAY) && (rep2 == ProglangType.STRING_ARRAY))))
      return false;

    if (debug.isLoggable(Level.FINE)) {
      debug.fine(
          "Checking isObviousSubSequenceDynamically " + subvar.name() + " in " + supervar.name());
    }

    Object[] di = isObviousSubSequence(subvar, supervar);
    if (di[1] != null) {
      inv.log("ObvSubSeq- true from isObviousSubSequence: " + di[1]);
      return true;
    }
    debug.fine("  not isObviousSubSequence(statically)");

    PptTopLevel ppt_parent = subvar.ppt;

    // If the elements of supervar are always the same (EltOneOf),
    // we aren't going to learn anything new from this invariant,
    // since each sequence should have an EltOneOf over it.
    if (false) {
      PptSlice1 slice = ppt_parent.findSlice(supervar);
      if (slice == null) {
        System.out.println("No slice: parent =" + ppt_parent);
      } else {
        System.out.println("Slice var =" + slice.var_infos[0]);
        for (Invariant superinv : slice.invs) {
          System.out.println("Inv = " + superinv);
          if (superinv instanceof EltOneOf) {
            EltOneOf eltinv = (EltOneOf) superinv;
            if (eltinv.num_elts() > 0) {
              inv.log(" obvious because of " + eltinv.format());
              return true;
            }
          }
        }
      }
    }

    // Obvious if subvar is always just []
    if (true) {
      PptSlice1 slice = ppt_parent.findSlice(subvar);
      if (slice != null) {
        for (Invariant subinv : slice.invs) {
          if (subinv instanceof OneOfSequence) {
            OneOfSequence seqinv = (OneOfSequence) subinv;
            if (seqinv.num_elts() == 1) {
              Object elt = seqinv.elt();
              if (elt instanceof long[] && ((long[]) elt).length == 0) {
                Debug.log(
                    debug, inv.getClass(), inv.ppt, vis, "ObvSubSeq- True from subvar being []");
                return true;
              }
              if (elt instanceof double[] && ((double[]) elt).length == 0) {
                inv.log("ObvSubSeq- True from subvar being []");
                return true;
              }
            }
          }
        }
      }
    }

    // Check for a[0..i] subseq a[0..j] but i < j.
    VarInfo subvar_super = subvar.isDerivedSubSequenceOf();
    VarInfo supervar_super = supervar.isDerivedSubSequenceOf();

    if (subvar_super != null && subvar_super == supervar_super) {
      // both sequences are derived from the same supersequence
      if ((subvar.derived instanceof SequenceScalarSubsequence
              || subvar.derived instanceof SequenceScalarArbitrarySubsequence)
          && (supervar.derived instanceof SequenceScalarSubsequence
              || supervar.derived instanceof SequenceScalarArbitrarySubsequence)) {
        VarInfo sub_left_var = null,
            sub_right_var = null,
            super_left_var = null,
            super_right_var = null;
        // I'm careful not to access foo_shift unless foo_var has been set
        // to a non-null value, but Java is too stupid to recognize that.
        int sub_left_shift = 42,
            sub_right_shift = 69,
            super_left_shift = 1492,
            super_right_shift = 1776;
        if (subvar.derived instanceof SequenceScalarSubsequence) {
          SequenceScalarSubsequence sub = (SequenceScalarSubsequence) subvar.derived;
          if (sub.from_start) {
            sub_right_var = sub.sclvar();
            sub_right_shift = sub.index_shift;
          } else {
            sub_left_var = sub.sclvar();
            sub_left_shift = sub.index_shift;
          }
        } else if (subvar.derived instanceof SequenceScalarArbitrarySubsequence) {
          SequenceScalarArbitrarySubsequence sub =
              (SequenceScalarArbitrarySubsequence) subvar.derived;
          sub_left_var = sub.startvar();
          sub_left_shift = (sub.left_closed ? 0 : 1);
          sub_right_var = sub.endvar();
          sub_right_shift = (sub.right_closed ? 0 : -1);
        } else {
          Assert.assertTrue(false);
        }
        if (supervar.derived instanceof SequenceScalarSubsequence) {
          SequenceScalarSubsequence super_ = (SequenceScalarSubsequence) supervar.derived;
          if (super_.from_start) {
            super_right_var = super_.sclvar();
            super_right_shift = super_.index_shift;
          } else {
            super_left_var = super_.sclvar();
            super_left_shift = super_.index_shift;
          }
        } else if (supervar.derived instanceof SequenceScalarArbitrarySubsequence) {
          SequenceScalarArbitrarySubsequence super_ =
              (SequenceScalarArbitrarySubsequence) supervar.derived;
          super_left_var = super_.startvar();
          super_left_shift = (super_.left_closed ? 0 : 1);
          super_right_var = super_.endvar();
          super_right_shift = (super_.right_closed ? 0 : -1);
        } else {
          Assert.assertTrue(false);
        }
        boolean left_included, right_included;
        if (super_left_var == null) left_included = true;
        else if (sub_left_var == null) // we know super_left_var != null here
        left_included = false;
        else
          left_included =
              VarInfo.compare_vars(
                  super_left_var, super_left_shift, sub_left_var, sub_left_shift, true /* <= */);
        if (super_right_var == null) right_included = true;
        else if (sub_right_var == null) // we know super_right_var != null here
        right_included = false;
        else
          right_included =
              VarInfo.compare_vars(
                  super_right_var,
                  super_right_shift,
                  sub_right_var,
                  sub_right_shift,
                  false /* >= */);
        //         System.out.println("Is " + subvar.name() + " contained in "
        //                            + supervar.name()
        //                            + "? left: " + left_included + ", right: "
        //                            + right_included);
        if (left_included && right_included) {
          inv.log("ObvSubSeq- True a[0..i] subseq a[0..j] and i < j");
          return true;
        }
      } else if ((subvar.derived instanceof SequenceStringSubsequence)
          && (supervar.derived instanceof SequenceStringSubsequence)) {
        // Copied from just above
        SequenceStringSubsequence sss1 = (SequenceStringSubsequence) subvar.derived;
        SequenceStringSubsequence sss2 = (SequenceStringSubsequence) supervar.derived;
        VarInfo index1 = sss1.sclvar();
        int shift1 = sss1.index_shift;
        boolean start1 = sss1.from_start;
        VarInfo index2 = sss2.sclvar();
        int shift2 = sss2.index_shift;
        boolean start2 = sss2.from_start;
        if (start1 == start2)
          if (VarInfo.compare_vars(index1, shift1, index2, shift2, start1)) {
            inv.log("True from comparing indices");
            return true;
          }
      } else {
        Assert.assertTrue(
            false,
            "how can this happen? "
                + subvar.name()
                + " "
                + subvar.derived.getClass()
                + " "
                + supervar.name()
                + " "
                + supervar.derived.getClass());
      }
    }

    // Also need to check A[0..i] subseq A[0..j] via compare_vars.

    // A subseq B[0..n] => A subseq B

    List<Derivation> derivees = supervar.derivees();
    // For each variable derived from supervar ("B")
    for (Derivation der : derivees) {
      // System.out.println("  ... der = " + der.getVarInfo().name() + " " + der);
      if (der instanceof SequenceScalarSubsequence) {
        // If that variable is "B[0..n]"
        VarInfo supervar_part = der.getVarInfo();
        // Get the canonical version; being equal to it is good enough.
        if (supervar_part.get_equalitySet_leader() == subvar) {
          Debug.log(debug, inv.getClass(), inv.ppt, vis, "ObvSubSeq- True from canonical leader");
          return true;
        }

        if (supervar_part.isCanonical()) {
          if (subvar == supervar_part) {
            System.err.println(
                "Error: variables "
                    + subvar.name()
                    + " and "
                    + supervar_part.name()
                    + " are identical.  Canonical");
            System.err.println(subvar.isCanonical());
            System.err.println(supervar_part.isCanonical());
            throw new Error();
          }

          // Check to see if there is a subsequence over the supervar
          if (ppt_parent.is_subsequence(subvar, supervar_part)) {
            if (Debug.logOn())
              inv.log(
                  "ObvSubSeq- true from A subseq B[0..n] "
                      + subvar.name()
                      + "/"
                      + supervar_part.name());
            return (true);
          }
        }
      }
    }
    return false;
  }
  /**
   * @return Array "a" such that a[0] is a valid discardCode and a[1] is a valid discardString. If
   *     the Invariant is not an obvious subsequence, both are null
   */
  public static Object[] isObviousSubSequence(VarInfo subvar, VarInfo supervar) {
    // Must typecheck since this could be called with non sequence variables in
    // some methods.
    ProglangType rep1 = subvar.rep_type;
    ProglangType rep2 = supervar.rep_type;
    if (!(((rep1 == ProglangType.INT_ARRAY) && (rep2 == ProglangType.INT_ARRAY))
        || ((rep1 == ProglangType.DOUBLE_ARRAY) && (rep2 == ProglangType.DOUBLE_ARRAY))
        || ((rep1 == ProglangType.STRING_ARRAY) && (rep2 == ProglangType.STRING_ARRAY)))) {
      return new Object[] {null, null};
    }

    if (debug.isLoggable(Level.FINE)) {
      debug.fine("isObviousSubSequence " + subvar.name() + "in " + supervar.name());
    }

    // Standard discard reason/string
    DiscardCode discardCode = DiscardCode.obvious;
    String discardString = subvar.name() + " obvious subset/subsequence of " + supervar.name();

    // For unions and intersections, it probably doesn't make sense to
    // do subsequence or subset detection.  This is mainly to prevent
    // invariants of the form (x subset of union(x, y)) but this means
    // we also miss those of the form (z subset of union(x,y)) which
    // might be useful.  Subsequence, however, seems totally useless
    // on unions and intersections.
    if (supervar.derived instanceof SequenceScalarIntersection
        || supervar.derived instanceof SequenceScalarUnion
        || subvar.derived instanceof SequenceScalarIntersection
        || subvar.derived instanceof SequenceScalarUnion) {
      discardCode = DiscardCode.obvious;
      discardString =
          "Invariants involving subsets/subsequences of unions/intersections" + "are suppressed";
      debug.fine("  returning true because of union or intersection");
      return new Object[] {discardCode, discardString};
    }

    if (subvar.derived instanceof SequencesPredicate) {
      // It's not useful that predicate(x[], b[]) is a subsequence or subset
      // of x[]
      SequencesPredicate derived = (SequencesPredicate) subvar.derived;
      if (derived.var1().equals(supervar)) {
        discardCode = DiscardCode.obvious;
        discardString = subvar.name() + " is derived from " + supervar.name();
        debug.fine("  returning true because of predicate slicing");
        return new Object[] {discardCode, discardString + " [pred slicing]"};
      }
    }

    VarInfo subvar_super = subvar.isDerivedSubSequenceOf();
    if (subvar_super == null) {
      // If it's not a union, intersection or a subsequence, it's not obvious
      debug.fine("  returning false because subvar_super == null");
      return new Object[] {null, null};
    }

    if (subvar_super == supervar) {
      // System.out.println("SubSequence.isObviousDerived(" + subvar.name() + ", " + supervar.name +
      // ") = true");
      // System.out.println("  details: subvar_super=" + subvar_super.name + "; supervar_super=" +
      // supervar.isDerivedSubSequenceOf() == null ? "null" :
      // supervar.isDerivedSubSequenceOf().name);
      discardCode = DiscardCode.obvious;
      discardString = subvar.name() + "==" + supervar.name();
      debug.fine("  returning true because subvar_super == supervar");
      return new Object[] {discardCode, discardString + " [subvar_super == supervar]"};
    }

    // a[i+a..j+b] cmp a[i+c..j+d]
    VarInfo supervar_super = supervar.isDerivedSubSequenceOf();
    // we know subvar_super != null due to check above
    if (subvar_super == supervar_super) {
      // both sequences are derived from the same supersequence
      if ((subvar.derived instanceof SequenceScalarSubsequence
              || subvar.derived instanceof SequenceScalarArbitrarySubsequence)
          && (supervar.derived instanceof SequenceScalarSubsequence
              || supervar.derived instanceof SequenceScalarArbitrarySubsequence)) {
        // In "A[i..j] subseq B[k..l]": i=sub_left_var, j=sub_right_var,
        //  k=super_left_var, l=super_right_var.
        VarInfo sub_left_var = null,
            sub_right_var = null,
            super_left_var = null,
            super_right_var = null;
        // I'm careful not to access foo_shift unless foo_var has been set
        // to a non-null value, but Java is too stupid to recognize that.
        int sub_left_shift = 42,
            sub_right_shift = 69,
            super_left_shift = 1492,
            super_right_shift = 1776;
        if (subvar.derived instanceof SequenceScalarSubsequence) {
          SequenceScalarSubsequence sub = (SequenceScalarSubsequence) subvar.derived;
          if (sub.from_start) {
            sub_right_var = sub.sclvar();
            sub_right_shift = sub.index_shift;
          } else {
            sub_left_var = sub.sclvar();
            sub_left_shift = sub.index_shift;
          }
        } else if (subvar.derived instanceof SequenceScalarArbitrarySubsequence) {
          SequenceScalarArbitrarySubsequence sub =
              (SequenceScalarArbitrarySubsequence) subvar.derived;
          sub_left_var = sub.startvar();
          sub_left_shift = (sub.left_closed ? 0 : 1);
          sub_right_var = sub.endvar();
          sub_right_shift = (sub.right_closed ? 0 : -1);
        } else {
          Assert.assertTrue(false);
        }
        if (supervar.derived instanceof SequenceScalarSubsequence) {
          SequenceScalarSubsequence super_ = (SequenceScalarSubsequence) supervar.derived;
          if (super_.from_start) {
            super_right_var = super_.sclvar();
            super_right_shift = super_.index_shift;
          } else {
            super_left_var = super_.sclvar();
            super_left_shift = super_.index_shift;
          }
        } else if (supervar.derived instanceof SequenceScalarArbitrarySubsequence) {
          SequenceScalarArbitrarySubsequence super_ =
              (SequenceScalarArbitrarySubsequence) supervar.derived;
          super_left_var = super_.startvar();
          super_left_shift = (super_.left_closed ? 0 : 1);
          super_right_var = super_.endvar();
          super_right_shift = (super_.right_closed ? 0 : -1);
        } else {
          Assert.assertTrue(false);
        }
        boolean left_included = false, right_included = false;
        if (super_left_var == null) left_included = true;
        if (super_left_var == sub_left_var) {
          if (super_left_shift < sub_left_shift) left_included = true;
        }
        if (super_right_var == null) right_included = true;
        if (super_right_var == sub_right_var) {
          if (super_right_shift > sub_right_shift) right_included = true;
        }
        if (left_included && right_included) {
          discardCode = DiscardCode.obvious;
          discardString = subvar.name() + " obvious subset/subsequence of " + supervar.name();
          return new Object[] {discardCode, discardString + " [obvious]"};
        }
      } else if ((subvar.derived instanceof SequenceStringSubsequence)
          && (supervar.derived instanceof SequenceStringSubsequence)) {
        // Copied from (an old version) just above
        // XXX I think this code is dead; why isn't it just produced
        // from the above by macro expansion? -smcc
        SequenceStringSubsequence sss1 = (SequenceStringSubsequence) subvar.derived;
        SequenceStringSubsequence sss2 = (SequenceStringSubsequence) supervar.derived;
        VarInfo index1 = sss1.sclvar();
        int shift1 = sss1.index_shift;
        boolean start1 = sss1.from_start;
        VarInfo index2 = sss2.sclvar();
        int shift2 = sss2.index_shift;
        boolean start2 = sss2.from_start;
        if (index1 == index2) {
          if (start1 == true && start2 == true) {
            if (shift1 <= shift2) return new Object[] {discardCode, discardString + " [shift1]"};
          } else if (start1 == false && start2 == false) {
            if (shift1 >= shift2) return new Object[] {discardCode, discardString + " [shift2]"};
          }
        }
      } else {
        Assert.assertTrue(
            false,
            "how can this happen? "
                + subvar.name()
                + " "
                + subvar.derived.getClass()
                + " "
                + supervar.name()
                + " "
                + supervar.derived.getClass());
      }
    }

    return new Object[] {null, null};
  }