Write a function to convert an infix expression to postfix (Reverse Polish Notat

```python
def infix_to_postfix(expression):
    precedence = {'+': 1, '-': 1, '*': 2, '/': 2, '^': 3}
    output = []
    stack = []
    for token in expression.split():
        if token.isalnum():
            output.append(token)
        elif token == '(':
            stack.append(token)
        elif token == ')':
            while stack and stack[-1] != '(':
                output.append(stack.pop())
            stack.pop()  # Remove the '('
        else:
            while stack and stack[-1] != '(' and precedence.get(token, 0) <= precedence.get(stack[-1], 0):
                output.append(stack.pop())
            stack.append(token)
    while stack:
        output.append(stack.pop())
    return ' '.join(output)

if __name__ == '__main__':
    infix_expression = "A + B * C - D / E"
    postfix_expression = infix_to_postfix(infix_expression)
    print(f"Infix Expression: {infix_expression}")
    print(f"Postfix Expression: {postfix_expression}")

    infix_expression = "( A + B ) * C - ( D - E ) * ( F + G )"
    postfix_expression = infix_to_postfix(infix_expression)
    print(f"Infix Expression: {infix_expression}")
    print(f"Postfix Expression: {postfix_expression}")
```