public UnconstrainedVariableCache(VariableConstraintGenerator constraintGenerator)
     : base(constraintGenerator) { }
 public PreserveEqualityCache(VariableConstraintGenerator constraintGenerator)
     : base(constraintGenerator) { }
 protected VariableCache(VariableConstraintGenerator constraintGenerator)
 {
     this.constraintGenerator = constraintGenerator;
 }