must riff
Regular verb: riff - riffed- riffed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must riff
you must riff
he must riff
we must riff
you must riff
they must riff 	I must be riffing
you must be riffing
he must be riffing
we must be riffing
you must be riffing
they must be riffing	I must have riffed
you must have riffed
he must have riffed
we must have riffed
you must have riffed
they must have riffed	I must have been riffing
you must have been riffing
he must have been riffing
we must have been riffing
you must have been riffing
they must have been riffing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't riff
you mustn't riff
he mustn't riff
we mustn't riff
you mustn't riff
they mustn't riff 	I mustn't be riffing
you mustn't be riffing
he mustn't be riffing
we mustn't be riffing
you mustn't be riffing
they mustn't be riffing	I mustn't have riffed
you mustn't have riffed
he mustn't have riffed
we mustn't have riffed
you mustn't have riffed
they mustn't have riffed	I mustn't have been riffing
you mustn't have been riffing
he mustn't have been riffing
we mustn't have been riffing
you mustn't have been riffing
they mustn't have been riffing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I riff?
must you riff?
must he riff?
must we riff?
must you riff?
must they riff? 	must I be riffing?
must you be riffing?
must he be riffing?
must we be riffing?
must you be riffing?
must they be riffing? 	must I have riffed?
must you have riffed?
must he have riffed?
must we have riffed?
must you have riffed?
must they have riffed? 	must I have been riffing?
must you have been riffing?
must he have been riffing?
must we have been riffing?
must you have been riffing?
must they have been riffing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I riff?
mustn't you riff?
mustn't he riff?
mustn't we riff?
mustn't you riff?
mustn't they riff? 	mustn't I be riffing?
mustn't you be riffing?
mustn't he be riffing?
mustn't we be riffing?
mustn't you be riffing?
mustn't they be riffing? 	mustn't I have riffed?
mustn't you have riffed?
mustn't he have riffed?
mustn't we have riffed?
mustn't you have riffed?
mustn't they have riffed? 	mustn't I have been riffing?
mustn't you have been riffing?
mustn't he have been riffing?
mustn't we have been riffing?
mustn't you have been riffing?
mustn't they have been riffing?