In the Cup_product article of Wikipedia:
It is possible to view the cup product as induced from the following composition: $$C^\bullet(X)\times C^\bullet(X)\to C^\bullet(X\times X)\overset{\Delta^*}\to C^\bullet(X)$$
How is $C^\bullet(X)\times C^\bullet(X)$ defined? Is it just a typo for $C^\bullet(X)\otimes C^\bullet(X)$?