existential verb 
Shows existence of something, same for singular and plural. Can be used with "'na' which causes soft mutation, eg: 'mae "na gaws", "oes 'na gaws?", "does 'na ddim caws". Note the mutation is blocked by 'ddim' in the negative. Na is used the same way for all tenses. Do not use with 'yn'.


present
"there is cheese"
aff (there is/are)		mae
int (is/are there?)		oes?
neg (there is/are not)	does dim
"yes"			oes
"no"	nag oes

imperfect (past)
"there was cheese"
aff	(r )oedd
int	oedd?
neg	doedd dim
"yes"	oedd
"no"	nag oedd

future
"there will be cheese"
aff	bydd
int	fydd?
neg	fydd dim
"yes"	bydd
"no"	na fydd