This is METAFONT, Version 2.71828 (Web2C 7.5.6) (base=mf 2012.4.18)  11 OCT 2014 09:10
**fort.51 fort.52 fort.71 fort.72 fort.73 fort.74 20141010-old-inf-end-betay/.
(fort.51
>> Change.in.coordinate.vector.due
! Isolated expression.
<to be read again> 
                   to
l.1 Change in coordinate vector due to
                                       upstream inflector scattering
? x