Annex G (informative) Ill-formed, no diagnostic required [ifndr]

G.10 [temp]: Templates [ifndr.temp]

G.10.5[ifndr:temp.constr.normal.invalid]
Specified in: [temp.constr.normal]

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If during constraint normalization any such substitution results in an invalid type or expression, the program is ill-formed, no diagnostic is required.
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[Example 1: template<typename T> concept A = T::value || true; template<typename U> concept B = A<U*>; template<typename V> concept C = B<V&>; // IFNDR, it would form the invalid type V&* // in the parameter mapping — end example]