private bool IsOperatorableNode(BaseFormulaNode node)
 {
     return(node is NumberNode ||
            node is VariableNode ||
            node is WordNode ||
            node is FunctionNode ||
            node is WordListNode ||
            node is NumberListNode);
 }
 private bool IsCloseBracket(BaseFormulaNode node)
 {
     return(node is BracketNode bracketNode && bracketNode.Bracket == Bracket.Close);
 }
 private bool IsOpenBracket(BaseFormulaNode node)
 {
     return(node is BracketNode bracketNode && bracketNode.Bracket == Bracket.Open);
 }