public Builder(Expression <Func <TGraph, TResult> > expression)
 {
     _from       = From;
     _expression = expression;
     _parameter  = (ParameterBinding <TGraph>)ParameterBinding.From(expression.Parameters[0]);
 }
 public LambdaBinding(ParameterBinding <TGraph> parameter, Binding <TResult> body)
 {
     _parameter           = parameter;
     _body                = body;
     _body.ResultChanged += (_, __) => MaybeOnResultChanged();
 }