 For each "i", choose a section "x""i" of "F" over "U""i".The projection map , which is loosely speaking the inclusion of the intersection of "U""i" and "U""j" in "U""i", induces a restriction map .If for all "i" and "j" the restrictions of "x""i" and "x""j" to are equal, then there must exist a unique section "x" of "F" over "U" which restricts to "x""i" for all "i".