A < in a markdown cell strips cell content when converting to latex

[jakobgager]

(in current master)
As the title says a < - not being part of an html tag - leads to the removal of the rest of the cell content or till a > character is found. The reason is the lxml package used for the citation2latex filter obviously treats the < as the begin of an html tag, and searches for the end tag.

citation2latex("1<2 is obviously true")

leads to

u'1'

and

citation2latex("A second line with 1<2 but here also 3>4 is present.")

leads to

u'A second line with 14 is present.'

Moreover the lxml package html-escapes some characters, see #4251