Use of a catalyst of the formula (I) where p is an integer from 1 to 6 and r is an integer from 0 to 5, where (p+r) is an integer from 1 to 6, L is a (p+r)-valent hydrocarbyl radical having a mean molecular weight in the range from 14 to 20'000 g/mol, optionally having heteroatoms, or is a (p+r+1)-valent hydrocarbyl radical having 4 to 12 carbon atoms, which together with Q' forms an optionally substituted 5- or 6-membered ring, or is a covalent bond, or is a hydrogen radical, Q is a reactive group selected from epoxide, aziridine, carbonate, carboxylic anhydride, carboxylic acid, carboxylic ester, lactone, carbonyl chloride, ketone, aldehyde, 1,3-diketone, 1,3-keto ester, 1,3-keto amide, cyanate, thiocyanate, isocyanate, isothiocyanate, (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, maleate, maleamide, maleimide, fumarate, fumaramide, itaconate, itaconamide, crotonate and crotonamide, Q' is a di- or trivalent connecting unit formed from the reaction of Q with HX, Y is N or X, where X is O or S or NR 3 , where R 3 is a hydrogen radical or is an alkyl or cycloalkyl or aralkyl radical which has 1 to 8 carbon atoms and optionally contains a tertiary amino group or a guanidine group, A is a divalent hydrocarbyl radical which has 2 to 30 carbon atoms and optionally contains unsaturated components and optionally ether oxygen or secondary or tertiary amine nitrogen, where A together with R 3 may also be a trivalent hydrocarbyl radical which has 5 to 10 carbon atoms and optionally contains a tertiary amine nitrogen, and Z is a guanidine group which is bonded via a nitrogen atom and does not contain any nitrogen atom which is bonded directly to an aromatic ring or is part of a heteroaromatic ring system, for the crosslinking of a curable composition. p is an integer from 1 to 6 and r is an integer from 0 to 5, where (p+r) is an integer from 1 to 6, L is a (p+r)-valent hydrocarbyl radical having a mean molecular weight in the range from 14 to 20'000 g/mol, optionally having heteroatoms, or is a (p+r+1)-valent hydrocarbyl radical having 4 to 12 carbon atoms, which together with Q' forms an optionally substituted 5- or 6-membered ring, or is a covalent bond, or is a hydrogen radical, Q is a reactive group selected from epoxide, aziridine, carbonate, carboxylic anhydride, carboxylic acid, carboxylic ester, lactone, carbonyl chloride, ketone, aldehyde, 1,3-diketone, 1,3-keto ester, 1,3-keto amide, cyanate, thiocyanate, isocyanate, isothiocyanate, (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, maleate, maleamide, maleimide, fumarate, fumaramide, itaconate, itaconamide, crotonate and crotonamide, Q' is a di- or trivalent connecting unit formed from the reaction of Q with HX, Y is N or X, where X is O or S or NR 3 , where R 3 is a hydrogen radical or is an alkyl or cycloalkyl or aralkyl radical which has 1 to 8 carbon atoms and optionally contains a tertiary amino group or a guanidine group, A is a divalent hydrocarbyl radical which has 2 to 30 carbon atoms and optionally contains unsaturated components and optionally ether oxygen or secondary or tertiary amine nitrogen, where A together with R 3 may also be a trivalent hydrocarbyl radical which has 5 to 10 carbon atoms and optionally contains a tertiary amine nitrogen, and Z is a guanidine group which is bonded via a nitrogen atom and does not contain any nitrogen atom which is bonded directly to an aromatic ring or is part of a heteroaromatic ring system, <EOS>