Rule 701.17f

If searching a zone is replaced with searching a portion of that zone, any other instructions that refer to searching the zone still apply. Any abilities that trigger on a library being searched will trigger. Example: Aven Mindcensor says, in part, “If an opponent would search a library, that player searches the top four cards of that library instead.” Veteran Explorer says “When Veteran Explorer dies, each player may search his or her library for up to two basic land cards and put them onto the battlefield. Then each player who searched his or her library this way shuffles it.” An opponent who searched the top four cards of his or her library because of Veteran Explorer’s ability would shuffle the entire library.

Find this number in the current Rules