Definitions for "Decision problem"
A problem in which all questions take the form ``Is something a member of a particular set?'' and all answers are either ``yes'' or ``no.''
a problem that takes as input some string and requires as output either YES or NO
a problem where all the answers are YES or NO
a countable set and a function
a finite set of lotteries that describe the feasible choices
a language L of strings over an alphabet
a subset of strings over the some alphabet
a system with all variables existentially quantified, that is, a system of the form where are all variables in