Pronormality is not finite-join-closed

Statement
A join of finitely many pronormal subgroups of a group need not be pronormal.

Facts used

 * 1) uses::Procharacteristicity is not finite-join-closed
 * 2) uses::Left residual of pronormal by normal is procharacteristic
 * 3) uses::Finite-join-closedness is left residual-preserved

Property-theoretic proof
The proof follows directly by combining facts (1)-(3).