Warning, this verb may not exist. Conjugation is given as example.
Affirmation
Simple form
I must keen keen you must keen keen she must keen keen we must keen keen you must keen keen they must keen keen
V-ing form
I must be keen keening you must be keen keening she must be keen keening we must be keen keening you must be keen keening they must be keen keening
Perfect
I must have keen keened you must have keen keened she must have keen keened we must have keen keened you must have keen keened they must have keen keened
V-ing perfect
I must have been keen keening you must have been keen keening she must have been keen keening we must have been keen keening you must have been keen keening they must have been keen keening
Negation
Simple form
I must not keen keen you must not keen keen she must not keen keen we must not keen keen you must not keen keen they must not keen keen
V-ing form
I must not be keen keening you must not be keen keening she must not be keen keening we must not be keen keening you must not be keen keening they must not be keen keening
Perfect
I must not have keen keened you must not have keen keened she must not have keen keened we must not have keen keened you must not have keen keened they must not have keen keened
V-ing perfect
I must not have been keen keening you must not have been keen keening she must not have been keen keening we must not have been keen keening you must not have been keen keening they must not have been keen keening
Interrogative form
Simple form
must I keen keen? must you keen keen? must she keen keen? must we keen keen? must you keen keen? must they keen keen?
V-ing form
must I be keen keening? must you be keen keening? must she be keen keening? must we be keen keening? must you be keen keening? must they be keen keening?
Perfect
must I have keen keened? must you have keen keened? must she have keen keened? must we have keen keened? must you have keen keened? must they have keen keened?
V-ing perfect
must I have been keen keening? must you have been keen keening? must she have been keen keening? must we have been keen keening? must you have been keen keening? must they have been keen keening?
Interro-negative form
Simple form
must I not keen keen? must you not keen keen? must she not keen keen? must we not keen keen? must you not keen keen? must they not keen keen?
V-ing form
must I not be keen keening? must you not be keen keening? must she not be keen keening? must we not be keen keening? must you not be keen keening? must they not be keen keening?
Perfect
must I not have keen keened? must you not have keen keened? must she not have keen keened? must we not have keen keened? must you not have keen keened? must they not have keen keened?
V-ing perfect
must I not have been keen keening? must you not have been keen keening? must she not have been keen keening? must we not have been keen keening? must you not have been keen keening? must they not have been keen keening?