t=3;

x=3+t;

y:=3+t

t=5; {x,y}

?x

?y

f[x_]:=x^6

?f

f[4]

f[4.]

f[4.0000000000000000000]

f[3.5]

f[7/2]

f[Pi]

f[Paolo]

(Paolo^6)//FullForm

Power[Paolo,6][[1]]

Paolo//Head

f["Paolo"]

(("Paolo")^6)//FullForm

Power["Paolo",6][[1]]//Head

f[Sin]

f[Sin[]]

f[1,2]

f[]

f[{1,2}]

Sin[.5]^6-f[Sin][.5]

?x

g[x]:=x^2

?g

g[2]

g[6]

g[6.]

g[2]:=Sin[6.]

?g

?f

f[2]:=-4

?f

f[2.]

f[2]

f[x_Integer]:= x^2

?f

f[2]

f[3]

f[4]

f[4.]

?f

Clear[f]

f[x_]:=x^6+Log[x^2]+1

Clear[y,t]

f'[t]

f''[t]

Integrate[f[t],t]

Integrate[f[t],{t,1,3}]

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

FindRoot[f[t]==0,{t,.5}]

?f

f[x_Integer]
x_Complex, Real, Symbol, List, String,

f[x_Integer] := n!

f[x_Real]:= Floor[x]

f[x_Complex]:= Abs[x]

?f

f'[t]

g[x_]:=
If[Head[x]==Integer, x!,
If[Head[x]==Real,Floor[x],
If...]

?Which

Which[(Subscript[test, 1]),(Subscript[value, 1]),(Subscript[test, 2]),(Subscript[value, 2]),…]

Which[
Head[x]==(Subscript[blah, 1]),(Subscript[expr, 1]),
Head[x]==(Subscript[blah, 2]),(Subscript[expr, 2]),
...
]

?Switch

Switch[expr,(Subscript[form, 1]),(Subscript[value, 1]),(Subscript[form, 2]),(Subscript[value, 2]),…]

Switch[
Head[x],
Integer, (Subscript[expr, 1]),
Real, (Subscript[expr, 2
]),
True, Print["something"]
]

p[x_/;x≤1]:=x^2-1

p[3]

p[1.]

Head[Pi]

Head[paolo]

p[Pi/10]

p[y_/;y>1]:=Exp[-y]-1/E

?p

Plot[p[t],{t,0,3}]

g[x_/;0≤x≤4]:=x

g[x_/;2≤x≤6]:=-x^2

g[3]

?g

h[x_/;2≤x≤6]:=-x^2

h[x_/;0≤x≤4]:=x

h[3]

?h

h[x_/;.5≤x≤1]:=0

?h

h[.5]

Clear[f]

f[x_]:= Sin[x]/x

Plot[f[t],{t,-3,3}]

f[0]

Limit[f[t],t->0]

f[0.]:=Limit[f[t],t->0]

?f

f[0]

f[0.]

Integrate[f[t],{t,0,1}]//N

Clear[f]

f[x_]:=Limit[Sin[t]/t,t->x]

?f

Plot[f[x],{x,-5,5}]

Clear[f]

f[x_]:=Sin[x]/x

f[0.]=Limit[f[x],x->0.];

?f