De Morgan ê hoat-chek ( Eng. De Morgan's laws) sī koan-î bīng-tē lô-chi̍p ê chi̍t-tùi hoat-chek, i hō· Eng-kok ê sò·-ha̍k-ka Augustus de Morgan hoat-hiān.
Iōng Venn tô͘ (Venn diagram) piáu-sī De Morgan ê hoat-chek. Teh tó chi̍t-chióng ê chêng-hóng hā, kiat-kó lóng sī līm-hô nâ-sek im-iáⁿ hā ê só͘-iú tiám chi chi̍p-ha̍p.
Tī chi̍p-ha̍p lāi-té:
(
A
∩
B
)
C
=
A
C
∪
B
C
{\displaystyle \left(A\cap B\right)^{C}=A^{C}\cup B^{C}}
(
A
∪
B
)
C
=
A
C
∩
B
C
{\displaystyle \left(A\cup B\right)^{C}=A^{C}\cap B^{C}}
Lán kah kun-kù ki-pún bēng-tê p, q ê līm-ì bēng-tê sǹg-hû P(o,q,...) ê tùi-giô tēng-gī chò:
¬
P
d
(
¬
p
,
¬
q
,
.
.
.
)
{\displaystyle \neg {\mbox{P}}^{d}(\neg p,\neg q,...)}