Link by cocopods with duplicate symbol error

[lgb1234a]

• Pod version : 1.8.4
• Xcode 11.2
• iPhone device 12.4.2

Podfile:
pod "CocoaMarkdown", :git => 'https://github.com/indragiek/CocoaMarkdown.git'

Link error:

duplicate symbol '_main' in:
    /Users/chenyn/Library/Developer/Xcode/DerivedData/CaJian-gdqwwrpegxglvygdepdetmfjtucl/Build/Intermediates.noindex/CaJian.build/Debug-iphoneos/CaJian.build/Objects-normal/arm64/main.o
    /Users/chenyn/Library/Developer/Xcode/DerivedData/CaJian-gdqwwrpegxglvygdepdetmfjtucl/Build/Products/Debug-iphoneos/cmark/libcmark.a(main.o)
ld: 1 duplicate symbol for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Is this an error related to my environment or resulted from any incorrect operation?