How to type theorem with automatic number by opmac

Question

It is quite convenient to use the opmac in Plain TeX, but I still do not know how to type a mathematical theorem with automatic number. At this stage, I am only able to type a theorem manually as:
input opmac

label[sec1]
sec Test 1
proclaim Theorem 1.1. This is a test of TeX.

sec Test 2
Refer to Section ref[sec1].

bye

It seems that above Theorem 1.1 can not be referred by "ref".
My question is how to type a slanted theorem with automatic number, so that I can refer it easily.
Any comments and suggestions will be appreciated.

egreg · Accepted Answer

If you want to preserve the awkward syntax of proclaim:
input opmac

newcounttheoremcount
defthetheoremcount{thetheoremcount}

deftheorem#1par{%
  globaladvancetheoremcount by 1
  csname proclaimendcsname
  Theorem wlabelthetheoremcountthetheoremcount. ignorespaces#1par
}

label[sec1]
sec Test 1

label[thm]
theorem This is a test of TeX.

sec Test 2
Refer to Section ref[sec1] and to theorem~ref[thm].

bye

The documentation of OPmac is rather scanty. If you want to link the theorem number to the section, you have to do it yourself.
input opmac

newcounttheoremcount
defthetheoremcount{thesecnum.thetheoremcount}
defsechook{globaltheoremcount=0 }

deftheorem#1par{%
  globaladvancetheoremcount by 1
  csname proclaimendcsname
  Theorem wlabelthetheoremcountthetheoremcount. ignorespaces#1par
}

label[sec1]
sec Test 1

label[thm]
theorem This is a test of TeX.

sec Test 2
Refer to Section ref[sec1] and to theorem~ref[thm].

label[thm2]
theorem This is a test of TeX.

Refer to theorem~ref[thm2].

bye

wipet · Answer

I borrowed the code from CTUstyle macro. Five independent registers A,B,C,D,E are declared here. We reset them in each section, see sechook definition below. They can be used in numbered paragraphs by macro numberedpar reg{Word}. For example
deftheorem {numberedpar A{Theorem}}
defcorollary {numberedpar A{Corollary}}
defexample {numberedpar B{Example}}
defnotice  {numberedpar C{Notice}}

This example shares numbers for Theorems and Colorraly and there are indepenent numbers for Examples and Notices.
The whole example is here:
input opmac

newcountnumA newcountnumB newcountnumC newcountnumD newcountnumE

defsechook#1relax{numA=0 numB=0 numC=0 numD=0 numE=0 
   seccnum=0 tnum=0 fnum=0 dnum=0 relax}

defnumberedpar#1#2{par globaladvancecsname num#1endcsname by1
   noindentwlabel{thesecnum.thecsname num#1endcsname}%
   {bf#2 thesecnum.thecsname num#1endcsname.}space}

deftheorem #1par{numberedpar A{Theorem}{it#1}}
defcorollary #1par{numberedpar A{Corollary}{it#1}}
defexample {numberedpar B{Example}}
defnotice  {numberedpar C{Notice}}

label[sec1]
sec Test 1
%proclaim Theorem 1.1. This is a test of TeX.

label[TheorX]
theorem This is Theorem.

sec Test 2
Refer to Section ref[sec1] and to Theorem ref[TheorX].

bye

How to type theorem with automatic number by opmac

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