Insert \allowbreak
where needed, or even better, reword the sentence - the breakpoints (after relations and binary operators) are there for a reason.
From TeX by Topic (p 207):
23.9 Line breaking in math formulas
In-line formulas can be broken after relations and binary operators. The respective penalties are the \relpenalty
and the \binoppenalty
. However, TeX will only break
after such symbols if they are not enclosed in braces. Other breakpoints can be created
with \allowbreak
, which is an abbreviation for \penalty0
.
Unlike in horizontal or vertical mode where putting two penalties in a row is equivalent to just placing the smallest one, in math mode a penalty placed at a break point
– that is, after a relation or binary operator – will effectively replace the old penalty
by the new one.
If you add \showoutput
to your MWE, you can see TeX printing the insertion of the penalty after the operator =
but nowhere else (the output below is for that $F_A(\pi_A) = F_A(\pi_{A},B)$ is
):
....\OT1/cmr/m/n/10 t
....\OT1/cmr/m/n/10 h
....\OT1/cmr/m/n/10 a
....\OT1/cmr/m/n/10 t
....\glue 3.33333 plus 1.66666 minus 1.11111
....\mathon
....\OML/cmm/m/it/10 F
....\hbox(4.78334+0.0)x6.51392, shifted 1.49998
.....\OML/cmm/m/it/7 A
....\OT1/cmr/m/n/10 (
....\OML/cmm/m/it/10 ^^Y
....\hbox(4.78334+0.0)x6.51392, shifted 1.49998
.....\OML/cmm/m/it/7 A
....\OT1/cmr/m/n/10 )
....\glue(\thickmuskip) 2.77771 plus 2.77771
....\OT1/cmr/m/n/10 =
....\penalty 500
....\glue(\thickmuskip) 2.77771 plus 2.77771
....\OML/cmm/m/it/10 F
....\hbox(4.78334+0.0)x6.51392, shifted 1.49998
.....\OML/cmm/m/it/7 A
....\OT1/cmr/m/n/10 (
....\OML/cmm/m/it/10 ^^Y
....\hbox(4.78334+0.0)x6.51392, shifted 1.49998
.....\OML/cmm/m/it/7 A
....\OML/cmm/m/it/10 ;
....\glue(\thinmuskip) 1.66663
....\OML/cmm/m/it/10 B
....\kern0.50172
....\OT1/cmr/m/n/10 )
....\mathoff
....\glue 3.33333 plus 1.66666 minus 1.11111
....\OT1/cmr/m/n/10 i
....\OT1/cmr/m/n/10 s
\allowbreak
at breakable locations might help.\allowlinebreak
but it was even more obvious.