<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def stacks_2_eqns(self,stacks):
 """returns equation strings from stacks"""

        if stacks:
            return list(map(lambda p: self.stack_2_eqn(p), stacks))
        else:
            return []