let a;
      console.log(a);
      a = 15;
      console.log(`Ma variable a = ${a}`);
      let b = 9;
      console.log(`Ma variable b = ${b}`);
      console.log(`${a} + ${b} = ${a + b}`);
      console.log(`${a} - ${b} = ${a - b}`);
      console.log(`${a} * ${b} = ${a * b}`);
      console.log(`${a} / ${b} = ${a / b}`);
      a = "Bonjour";
      b = "les amis";
      console.log(a + b);
      console.log(`${a} ${b}`);
      a = true;
      b = false;
      console.log(`${a} AND ${b} = ${a && b}`);
      console.log(`${a} AND ${b} = ${a || b}`);
      a = new Date(Date.now());
      b = new Date(a);
      b.setDate(-61);
      console.log(a.toLocaleString() + " | " + b.toLocaleString());
   
      a = Math.PI;
      b = "bonjour";
      let c = true;
      let d = new Date(Date.now());
      let e;
      let f = 12345678987654321n;
   
      console.log("a = " + typeof a);
      console.log("b = " + typeof b);
      console.log("c = " + typeof c);
      console.log("d = " + typeof d);
      console.log("e = " + typeof e);
      console.log("f = " + typeof f);