public override T Accept <T>(INodeExprVisitor <T> visitor) => visitor.Visit(this);
public virtual T Accept <T>(INodeExprVisitor <T> visitor) => visitor.Visit(this);
public override T Accept <T>(INodeExprVisitor <T> visitor) => (visitor is INodeExprVisitor <N, T>) ? ((INodeExprVisitor <N, T>)visitor).Visit(this) : visitor.Visit(this);