úÎÒNone"#$]^Ä@a operators list which cantains a list in order with precedence.9parse a infix expression to prefix expression in a stack.get a sub string index sub string origin String(prefix index, postfix index).prefix-expression-1.2.2-LbivbC1x9Xt4yFUMLU6OmQText.Exp.Prefix fromInfix expOperators elemSubIndex