[temp.constr.fold]

A fold expanded constraint whose fold-operator is && is satisfied if it is a valid pack expansion and if

N = 0 or if for each i where 0 \leq i < N in increasing order, C is satisfied when replacing each pack expansion parameter with the corresponding {i th element .}^{th element .}

No substitution takes place for any i greater than the smallest i for which the constraint is not satisfied.

A fold expanded constraint whose fold-operator is || is satisfied if it is a valid pack expansion,

N > 0, and if for i where 0 \leq i < N in increasing order, there is a smallest i for which C is satisfied when replacing each pack expansion parameter with the corresponding {i th element .}^{th element .}

No substitution takes place for any i greater than the smallest i for which the constraint is satisfied.

[Note 1:

If the pack expansion expands packs of different size, then it is invalid and the fold expanded constraint is not satisfied.

— end note]

Two fold expanded constraints are compatible for subsumption if their respective constraints both contain an equivalent unexpanded pack ([temp.over.link]).