Proof about a theorem that says a function is continuous if only if f is right continuous in a and left continuous.
Clash Royale CLAN TAG #URR8PPP up vote 1 down vote favorite Theorem : A function $f:Dto mathbb R$ is continuous in $ain D$ $iff f$ is left and right continuous in $a$. Proof: I firstly thought just to write down the definitions of left and right continuous and then it trivially shows the theorem. But apparently it isn't sufficient. Let $f:Dtomathbb R$ and consider $ain D$. The function $f$ is rightcontinuous in $a iff$ $$(forallepsilongt 0)(existsdeltagt 0)(ale xlt a+deltaRightarrow |f(x)-f(a)|ltepsilon)$$ and left continous $iff$ $a iff$ $$(forallepsilongt 0)(existsdeltagt 0)(a -deltalt xle aRightarrow |f(x)-f(a)|ltepsilon)$$ So I found a proof online on this webpage. My question is there another way to prove this maybe with the use of my definitions? I'd most appreciate it. calculus proof-writing alternative-proof epsilon-delta share | cite | improve this question edited Aug 24 at 11:10 asked Aug 24 at 10:38 Anonymous I 835 1 7 2...