Full Idea
<a,b> is a set whose members occur in the order shown; <x1,x2,x3, ..xn> is an 'n-tuple' ordered set.
Clarification
note that the brackets are angled
Gist of Idea
<a,b&62; is a set whose members occur in the order shown
Source
Graham Priest (Intro to Non-Classical Logic (1st ed) [2001], 0.1.10)
Book Reference
Priest,Graham: 'Introduction to Non-Classical Logic' [CUP 2001], p.-6