Mfcttrf

I'd like to change the theorem environment headfont to match komascript's fonts in chapters and sections. Particularly I'm interested in knowing how to do this using packages like thmtools.

Here's the MWE:

documentclassscrbook
usepackage[utf8]inputenc
usepackageamsmath
newtheoremthmTheorem
begindocument
sectionIntroduction to the theorem

Introduction of something. Here's the theorem:

beginthm
This is a theorem.
endthm

enddocument

Here's the output

With amsthm, looking at https://tex.stackexchange.com/a/17555/4427 where the standard values are listed:

documentclassscrbook
usepackage[utf8]inputenc
usepackageamsmath
usepackageamsthm

newtheoremstylekomaplain
 topsep % ABOVESPACE
 topsep % BELOWSPACE
 itshape % BODYFONT
 0pt % INDENT (empty value is the same as 0pt)
 bfseriessffamily % HEADFONT
 . % HEADPUNCT
 5pt plus 1pt minus 1pt % HEADSPACE
 % CUSTOM-HEAD-SPEC

theoremstylekomaplain
newtheoremthmTheorem

begindocument

sectionIntroduction to the theorem

Introduction of something. Here's the theorem:

beginthm
This is a theorem.
endthm

beginthm[Note]
This is a theorem.
endthm

enddocument

Using thmtools you can change the headfont as follows:

documentclassscrbook
usepackage[utf8]inputenc
usepackageamsmath,amsthm

usepackagethmtools
declaretheoremstyle[headfont=sffamilybfseries]thm
declaretheorem[style=thm]thm

begindocument
sectionIntroduction to the theorem

Introduction of something. Here's the theorem:

beginthm
This is a theorem.
endthm

enddocument

Here is an example code with amsthm and thmtools. Note that thmtools also cooperates with ntheorem:

documentclassscrbook
usepackage[utf8]inputenc
usepackageamsmath
usepackageamsthm, thmtools
newtheoremthmTheorem
declaretheoremstyle[%
spaceabove=6pt, spacebelow=6pt,%
headfont=sffamilybfseries,
notefont=sffamilybfseries, notebraces=(),
headpunct =,—,
bodyfont=normalfontitshape]%
sf
declaretheorem[style=sf, within=chapter, name=Theorem]theo

begindocument

setcounterchapter3
sectionIntroduction to the theorem

Introduction of something. Here's the theorem:

begintheo[using a sans font]
This is a well-known theorem.
endtheo

enddocument 

To ensure that headfont matches the font settings of chapter and section titles in a KOMA-Script document use

usekomafontdisposition

The initial definition for the disposition font element is normalcolorsffamilybfseries. But this can be changed using setkomafont or addtokomafont.

documentclassscrbook
PreventPackageFromLoadingremreset% comment this line, if you use an older TeX-Distribution
usepackage[utf8]inputenc
usepackageamsmath,amsthm

%addtokomafontdispositionrmfamily

usepackagethmtools
declaretheoremstyle[headfont=usekomafontdisposition]thm
declaretheorem[style=thm]thm

begindocument
sectionIntroduction to the theorem

Introduction of something. Here's the theorem:

beginthm[Note]
This is a theorem.
endthm

enddocument

Additional remark: thmtools loads package remreset which is obsolete with uptodate TeX distributions. To avoid the resulting warning »The remreset package is obsolete: @removefromreset is defined.« KOMA-Script command PreventPackageFromLoadingremreset is used in the example.