2 % home made blackboard-bold symbols: B C D E F G H I J K L M N O P Q R T U Z
5 \def\bbbB{{{\rm I}\mkern-3.8mu{\rm B}}}
6 \def\bbbC{{{\rm C}\mkern-15mu{\phantom{\rm t}\vrule}\mkern9mu}}
7 \def\bbbD{{{\rm I}\mkern-3.8mu{\rm D}}}
8 \def\bbbE{{{\rm I}\mkern-3.8mu{\rm E}}}
9 \def\bbbF{{{\rm I}\mkern-3.8mu{\rm F}}}
10 \def\bbbG{{{\rm G}\mkern-16mu{\phantom{\rm t}\vrule}\mkern10mu}}
11 \def\bbbH{{{\rm I}\mkern-3.8mu{\rm H}}}
12 \def\bbbI{{{\rm I}\mkern-12mu{\phantom{\rm t}\vrule}\mkern6mu}}
13 \def\bbbJ{{{\rm J}\mkern-12mu{\phantom{\rm t}\vrule}\mkern6mu}}
14 \def\bbbK{{{\rm I}\mkern-3.8mu{\rm K}}}
15 \def\bbbL{{{\rm I}\mkern-3.8mu{\rm L}}}
16 \def\bbbM{{{\rm I}\mkern-3.8mu{\rm M}}}
17 \def\bbbN{{{\rm I}\mkern-3.8mu{\rm N}}}
18 \def\bbbO{{{\rm O}\mkern-16mu{\phantom{\rm t}\vrule}\mkern10mu}}
19 \def\bbbP{{{\rm I}\mkern-3.8mu{\rm P}}}
20 \def\bbbQ{{{\rm Q}\mkern-16mu{\phantom{\rm t}\vrule}\mkern10mu}}
21 \def\bbbR{{{\rm I}\mkern-3.8mu{\rm R}}}
22 \def\bbbT{{{\rm T}\mkern-16mu{\phantom{\rm t}\vrule}\mkern10mu}}
23 \def\bbbU{{{\rm U}\mkern-15mu{\phantom{\rm t}\vrule}\mkern9mu}}
24 \def\bbbZ{{{\sf Z}\mkern-7.5mu{\sf Z}}}