«La» commonly negates an imperfect-form verb in the present or gives a general denial. «Ma» is used across differing constructions and time reference. Negative «in» must be distinguished from conditional «in».
Compare «لا يقوم زيدٌ» (negation of standing) with «إن يقمْ زيدٌ أكرمْهُ» (conditional consequence). The second does not itself assert the non-occurrence of standing.