Input : list of pairs

in=RandomInteger[{10,20},{20,2}]

noDup[
{l___,{a_,b_},m___,{a_,b_},r___}
]:=noDup[{l,{a,b},m,r}]

noDup[x_]:=x

noDup[in]//Length

noDup2[
{l___,p:{a_,b_},m___,q:{c_,d_},r___}
]/;p==q:=noDup2[{l,p,m,r}]

noDup2[x_]:=x

noDup2[in]//Length

noDup3[
{l___,p:{a_,b_},m___,p,r___}
]:=noDup3[{l,p,m,r}]

noDup3[x_]:=x

noDup3[in]//Length

noDup4[
{l___,p:{a_,b_},m___,{a_,b_},r___}
]:=noDup4[{l,p,m,r}]

noDup4[x_]:=x

noDup4[in]//Length

in

Union[in]//Length

DeleteDuplicates

in=RandomInteger[{10,20},{30,2}]

Duplicates : {a,b}=={a,b};    {a,b}=={b,a}

Clear[noDup]

noDup[
{l___,{a_,b_},m___,{a_,b_},r___}
]:=noDup[{l,{a,b},m,r}]

noDup[
{l___,{a_,b_},m___,{b_,a_},r___}
]:=noDup[{l,{a,b},m,r}]

noDup[x_]:=x

{in//Sort//ColumnForm,noDup[in]//Sort//ColumnForm}

in=RandomInteger[{-10,10},40]

seq[{l___,m___,r___}]/;
Apply[Plus,{m}]==k:={m}

k=5; seq[in]

seq[{l___,a_,m___,b_,r___}]/;a+b==k:={m}

k=6; seq[in]

Clear[seq]

seq=Table[{α,β}[[RandomInteger[]+1]],{100}]

seq=Table[{{α,β}[[RandomInteger[]+1]],1},{100}]

compact[
{l___,{symb_,n_},{symb_,m_},r___}]:=
compact[{l,{symb,m+n},r}]

compact[x_]:=x

compact[seq]//ColumnForm

func[{input_},output_]:=
func[{input'},Join[output,{}]]

func[input,{}]

func[x_,out_]:=out

Join[{a,b,c,d},{3}]

Join[{a,b,c,d},{3,2,1}]

f[x_]:=Sin[Exp[x/10]+Sin[7 x]]

Plot[f[t],{t,0,2}]

eval={};

auxF[x_]:=
(eval=Join[eval,{x}];
f[x])

p=Plot[auxF[t],{t,0,2}]

Length[eval]

ListPlot[eval]

ListPlot[Sort[eval]]

ListPlot[Map[f,Sort[eval]]]

lp=ListPlot[Map[{#,f[#]}&,Sort[eval]],PlotStyle->Red]

Show[{p,lp}]

#^2&

#^2&[Pi]

Clear[l,f]

l={Pi,0.,a,b,{},hh[1,2^t],{-5,4,c}};

Map[f,{1,2,3,4,5}]

Apply[f,a b c d e]

Map[f,a b c d e]

TreeForm[a b c d e]

Map

f/@{1,2,3,4,5}

Apply

f@@{1,2,3,4,5}

Function call

f@{1,2,3,4,5}

l

Map[h,l]//TreeForm

Map[h,l,{2}]

Map[h,l,{2}]//TreeForm

mat=
{{1,2,3},
{a,b,c},
{α,β,γ}};

mat//MatrixForm

Map[v,mat]//MatrixForm

Map[v,mat,{2}]//MatrixForm

l

Map[v,l]
Map[v&,l]
Map[v[#],l]
Map[v[#]&,l]

#1+#2^2&[1,2]

l=RandomInteger[{10^2,10^3},{21}]

Map[PrimeQ,l]

Map[{#,PrimeQ[#]}&,l]

Select[
Map[{#,PrimeQ[#]}&,l],
#[[2]]&
]

Select[l,PrimeQ]

Select[l,PrimeQ[#]&]

Map[{#,Mod[#,19]==0}&,l]

l  -> {x, Exp[x]}

Map[{#,Exp[#]}&,l]

l   -> Sin[#]^x&

Map[ Sin[#]^#&,l]

Map[ Sin[#]^x_&,l]

Function[{x},x^2]

Function[{x},x^2][3]

Map[ Function[{t},Sin[t]^#]&,l][[3]][3.]

Sin[3.]^625