*\input basic
 (basic.TEX 1 2 3 4)
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etc.
⊗⊗⊗ nesting level 0
! OK.
(*) $x:=x+1$\par\ddt

↑
*\trace'77777777\ddt
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⊗⊗⊗ nesting level 0
! OK.
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↑
*\chcode'272←'3072
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(*) $x:=x+1$\ddt

↑e
Type <cr> to continue, <lf> to flash error messages,
	1 or ... or 9 to ignore the next 1 to 9 tokens of input,
	i or I to insert something, x or X to quit.
↑t
Type <cr> to continue, <lf> to flash error messages,
	1 or ... or 9 to ignore the next 1 to 9 tokens of input,
	i or I to insert something, x or X to quit.
↑i
*\input test 
! You can't do that in horizontal mode.
(*) \input
 test 
(*) $x:=x+1$\ddt

↑9
*\par\input test
(*) \par\input te
st
↑
*\par\input test
 (test.TEX 1 2 3


! Undefined control sequence.
p.3,l.2 This is line 2 of page 4 \error

↑e