Specific forms of the mark include rounded brackets (also named parenthesis), square brackets, curly brackets (also named braces), and angle brackets (also named chevrons), as well as various less common pairs of symbols. typically deployed in symmetric pairs, an individual bracket may be identify as a left or right bracket or, alternatively, an opening paired bracket or closing paired bracket, respectively, depending on the directionality of the context. Chevrons, ⟨ ⟩, were the earliest type of bracket to look in write English. Desiderius Erasmus coined the term lunula to refer to the rounded parenthesis, (), recalling the shape of the crescent moon.

COMING SOON!

```
"""
The nested brackets problem is a problem that determines if a sequence of
brackets are properly nested. A sequence of brackets s is considered properly nested
if any of the following conditions are true:
- s is empty
- s has the form (U) or [U] or {U} where U is a properly nested string
- s has the form VW where V and W are properly nested strings
For example, the string "()()[()]" is properly nested but "[(()]" is not.
The function called is_balanced takes as input a string S which is a sequence of brackets and
returns true if S is nested and false otherwise.
"""
def is_balanced(S):
stack = []
open_brackets = set({"(", "[", "{"})
closed_brackets = set({")", "]", "}"})
open_to_closed = dict({"{": "}", "[": "]", "(": ")"})
for i in range(len(S)):
if S[i] in open_brackets:
stack.append(S[i])
elif S[i] in closed_brackets:
if len(stack) == 0 or (
len(stack) > 0 and open_to_closed[stack.pop()] != S[i]
):
return False
return len(stack) == 0
def main():
S = input("Enter sequence of brackets: ")
if is_balanced(S):
print((S, "is balanced"))
else:
print((S, "is not balanced"))
if __name__ == "__main__":
main()
```