Using ifelse in cmake

hi!

I am a technical writer and I have a book that works approximately as follows:

set(Installation_Name

Installation/Chapter1.md
Installation/Chapter2.md

)

add_custom_command(OUTPUT Installation_Output

COMMAND cat ${Installation_Name} > Book.md
COMMAND ${Pandoc_Command_Version} Book.md -o Book.pdf
WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/src/MD/" 
		VERBATIM
		)

add_custom_target(MyDocs ALL DEPENDS Installation_Output)
install(FILES 
${CMAKE_CURRENT_SOURCE_DIR}/src/MD/Book.pdf

I want to make a construction that allows me to do something like that:

set(Installation_Name

Installation/Chapter1.md
Installation/Chapter2.md
)

if(${WORKING_DIRECTORY} STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}/src/MD/")
set(Installation_Name
		Installation/Chaper3.md 
		)
elseif(${WORKING_DIRECTORY} STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}/src/MD_special/")
	set(Installation_Name
		Special_Installation/Chaper4.md 
		)
endif()
)

set(Installation_Name
Installation/Chapter5.md
Installation/Chapter6.md

)

...

that is, I need the cmake file to start fulfilling the conditions: if the directory is “src/MD/”, then use the “Installation/Chaper3.md” chapter, and if the directory is different, then use another chapter
I tried to use the above code (I wrote it approximately), but I’m not very familiar with the cmake syntax yet and obviously made a mistake somewhere
Please tell me how can I execute this scenario and what am I doing wrong?

What is “WORKING_DIRECTORY” here? Where are you expecting it to come from?