Weeks had passed as if a river stream had just rapidly flowed. At Wilford's personal field, Lucas was sitting in a meditative pose as he laid a portable array on his seat.
A portable array is some kind of combination of magic and array, but the main concept here was magic, as there were plenty of ways to bring portable spells which Lucas improvised.
A portable paper is a type of paper created by magic that has a unique complex of properties that allow it to hold spells and magical runes without harming its use. Of course, anyone could just create another spell, but the purpose of this portable paper was to put a one-time-use spell on the paper. In this world, it is the equivalent of a talisman.
Thus, after some improvisation, Lucas put an array instead of a spell to make use of it even in different places.