a+[3a-5a-{2a-(5a-5b)}]
2a-5b
a+(3a-5a-(2a-5a+5b))
a+(3a-5a-(-3a+5b))
a+(3a-5a+3a-5b)
a+(6a-5a-5b)
a+(a-5b)
2a-5b.
