@Nullable AnalysisStartingPoint tryJoin(@NotNull AnalysisStartingPoint next) {
    if (!EquivalenceChecker.getCanonicalPsiEquivalence().expressionsAreEquivalent(this.myAnchor, next.myAnchor)) return null;
    DfType meet = this.myDfType.join(next.myDfType);
    if (meet == DfType.TOP) return null;
    return new AnalysisStartingPoint(meet, this.myAnchor);
  }
@Nullable AnalysisStartingPoint tryJoin(@NotNull AnalysisStartingPoint next)