Hi, I hopped you all had a merry Christmas :-) In the very first working example: \definefontfamily [mainface] [rm] [Latin Modern Roman] \definefallbackfamily [mainface] [mm] [TeX Gyre Termes Math] [range={uppercasedoublestruck}] %%%,letterlikesymbols}] \definefontfamily [mainface] [mm] [Latin Modern Math] \setupbodyfont[mainface] \starttext \startformula ABC \quad {\blackboard AB[C]DEFG[H]IJKLM[N]O[PQR]STUVWXY[Z]} \stopformula \stoptext letters here in brackets weren't rendered as expected... Because there are "holes in the uft table" as can be seen there: http://www.w3.org/TR/MathML2/double-struck.html Adding the "bloks" "letterlikesymbols" was, to an extent solving the problem. Now in my document I am also using calligraphic letters which I want to remain in "modern". 1- WHAT DIDN'T WORK: First idea that comes to me is modifying the file: math-act.lua I have added all the lines that are commented out here. blocks["uppercasedoublestruck"] = { first = 0x1D538, last = 0x1D550 } %0x1D551 is not attributed %blocks["uppercasedoublestruckc"] = { first = 0x02102, last = 0x02102 } % %blocks["uppercasedoublestruckh"] = { first = 0x0210D, last = 0x0210D } % %blocks["uppercasedoublestruckn"] = { first = 0x02115, last = 0x02115 } % %blocks["uppercasedoublestruckp"] = { first = 0x02119, last = 0x02119 } % %blocks["uppercasedoublestruckq"] = { first = 0x0211A, last = 0x0211A } % %blocks["uppercasedoublestruckr"] = { first = 0x0211D, last = 0x0211D } % %blocks["uppercasedoublestruckz"] = { first = 0x02124, last = 0x02124 } % It just didn't work. Compiled but fail to provided expected result: Everything was in modern. 2- WHAT WORKED \definefontfamily [mainface] [rm] [Latin Modern Roman] \definefallbackfamily [mainface] [mm] [TeX Gyre Termes Math] [range={uppercasedoublestruck,0x02102,0x0210D,0x02115,0x02119,0x0211A,0x0211D,0x02124}] \definefontfamily [mainface] [mm] [Latin Modern Math] \setupbodyfont[mainface] \starttext \startformula \int_a^b \quad ABC \quad {\blackboard AB[C]DEFG[H]IJKLM[N]O[PQR]STUVWXY[Z]} \stopformula \stoptext 3-QUESTION Unless I'm completely wrong, the modification I've made to the file: math-act.lua haven't been taken into account at all: even if I modify the line "uppercasedoublestruck" such as to reduce the range: blocks["uppercasedoublestruck"] = { first = 0x1D538, last = 0x1D540 } my \blackboard UVXY keep to be rendered with term... So why? Regards, Chris