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-1.0.2-JHaV9o0AhJVDtQ9pX7MaHWText.Exp.Prefix fromInfix expOperators elemSubIndex