Add -er for the comparative and -st for the superlative.
Use the comparative with dan (vaster dan…) and the superlative with het (het vastste).
The comparative (vergrotende trap) of vast is vaster. Add -er for the comparative and -st for the superlative. Use it with 'dan': ...vaster dan...
The superlative (overtreffende trap) of vast is vastst, usually used as het vastste.
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